Helium Spotted in Moon's Wispy Atmosphere

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A NASA spacecraft has detected helium in the moon's tenuous
atmosphere, confirming observations made four decades ago on the
lunar surface.

NASA's
Lunar Reconnaissance Orbiter (LRO) sniffed out the helium
from above with an onboard spectrometer. The finding corroborates
measurements made by the Lunar Atmosphere Composition Experiment
(LACE), which was deployed by moonwalking Apollo 17 astronauts in
1972.

"The question now becomes, does the helium originate from inside
the moon — for example, due to radioactive decay in rocks —
or from an exterior source, such as the solar wind?" Alan Stern,
of the Southwest Research Institute in Boulder, Colo., said in a
statement. Stern is principal investigator of LRO's Lyman Alpha
Mapping Project spectrometer, or LAMP.

While LAMP is primarily a surface-mapping tool, researchers used
the instrument to study the moon's thin atmosphere over a
campaign lasting more than 50 orbits. They detected helium, then
applied several different techniques to confirm that LAMP wasn't
just picking up gas in the interplanetary background. [ 10
Coolest Moon Discoveries by LRO ]

Further LAMP observations could help scientists nail down the
dominant source of the helium, Stern said.

"If we find the solar wind is responsible, that will teach us a
lot about how the same process works in other airless bodies,"
Stern said.

The LACE measurements from the 1970s showed an increase in helium
abundance as night progressed, a result that could be explained
by atmospheric cooling (which concentrates atoms at lower
altitudes). LAMP should build on those findings by investigating
how helium abundances vary with latitude, researchers said.

The $504 million LRO probe launched in June 2009 along with a
piggyback spacecraft called LCROSS. In October of that year,
LCROSS slammed intentionally into a shadowed crater at the moon's
south pole, unearthing lots
of water ice.

LRO is about the size of a Mini Cooper, and it carries seven
instruments to observe the moon. The spacecraft circles the
moon in a polar orbit, at an altitude of about 31 miles (50
kilometers).

For the first year of its operational life, LRO scouted the moon
to help NASA plan for future lunar exploration missions. In
September 2010, the probe wrapped up this mission and shifted
into a pure science mode.

"These ground-breaking measurements were enabled by our flexible
operations of LRO as a science mission, so that we can now
understand the moon in ways that were not expected when LRO was
launched in 2009," said Richard Vondrak, LRO project scientist at
NASA’s Goddard Space Flight Center in Greenbelt, Md.

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